
#include <atomic>
#include <thread>
#include <assert.h>

std::atomic<bool> x,y;
std::atomic<int> z;

void write_x_then_y()
{
  x.store(true,std::memory_order_relaxed);
  y.store(true,std::memory_order_relaxed);
}

void read_y_then_x()
{
  while(!y.load(std::memory_order_relaxed));
  if(x.load(std::memory_order_relaxed))
    ++z;
}

int main()
{
  x=false;
  y=false;
  z=0;
  std::thread a(write_x_then_y);
  std::thread b(read_y_then_x);
  a.join();
  b.join();
  assert(z.load()!=0);
}
